Composite filter medium and fluid filters containing same

ABSTRACT

A composite filter medium for removing at least 99.95 percent of particulates of a size in the 3 to 4 micron range and dissolved chemical contaminants from a fluid and filters of various configurations employing the composite filter medium are disclosed. The composite filter medium comprises an adsorbent layer containing an adsorbent agent and a hydrophilic particulate intercepting layer disposed adjacent to the adsorbent layer. The composite medium has a mean flow pore diameter of about 1 to 10 microns, a bubble point of about 3 to 15 microns and an air permeability of about 0.5 to 7 liters per minute/cm 2  with a pressure drop of about 0.1 bar.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to filters and filter media. Moreparticularly, the present invention relates to a composite filter mediafor filtering contaminants from a fluid and fluid filters containing thecomposite filter medium.

2. Description of the Prior Art

Fluids, such as liquids or gases, typically contain contaminants whichinclude particulates, chemicals, and organisms. In many cases, it isdesirable to remove some or all of such contaminants from the fluid.Usually, contaminants are removed from a fluid supply by passing thefluid through a filter whereby the contaminants are separated from thefiltered fluid or filtrate.

Water is probably the most highly filtered fluid as it is filtered inindustrial processes as well as in the household. Purification of waterto produce potable water often requires the simultaneous reduction ofparticulate contaminants, dissolved organic chemicals and inorganicheavy metals. Particulate contaminants may include dirt, rust, silt, andother particles as well as potentially hazardous microorganisms such aschlorine resistant protozoan cysts, such as Cryptosporidium Parvum orGiardia, or bacteria such as Cholera and E. coli. Organic chemicals mayinclude those that contribute to taste and odor as well as potentiallytoxic pesticides, chlorinated hydrocarbons, and other synthetic organicchemicals. Free chlorine reduction is also a major objective when theresidual concentration of this disinfectant is sufficiently high tocause a bad taste. The most common heavy metal found in domestic wateris lead derived from brass fixtures, leaded solder, lead pipes or othersources. Other heavy metals often found in drinking water includecopper, zinc, manganese and iron.

The most common household water filters are typically small trapezoidalshaped plastic containers filled with a loose adsorbent medium such asactivated carbon, ion exchange resins or zeolites. Water is filtered bysuch water filters by passing it through the loose adsorbent medium inan axial direction from a wider to a narrower portion of the trapezoidalcontainer.

The trapezoidal shaped filter element is often used in a carafe and whenused in a carafe is typically called a gravity-flow carafe filter. Suchfilters are typically installed within a household carafe having anupper reservoir, a lower reservoir and a filter receptacle fitted at thebottom of the upper reservoir. The trapezoidal shaped filter element isinstalled in the carafe by wedging it into the receptacle so as toeffect a seal between the two reservoirs. Water passing from the upperreservoir to the lower reservoir must pass through the filter element.Typically, water enters the filter element through a series of smallperforations at the wider top of the trapezoid. The water flows throughthe filter to the narrower bottom while traversing the porous bed ofloose adsorbent. The water passes through a series of micro perforationsin the narrower bottom of the filter exiting into the lower reservoir.In some filters, one or more non-woven pads, functioning as a finesfilter, may be installed at the bottom, top or both bottom and top ofthe filter element to prevent the release of fine particles from theadsorbent bed.

The flow rate through present day gravity-flow carafe filters asdescribed above is generally slow, typically about 200 ml per minute fora filter loaded with 100 grams of mixed wet resin-carbon filter mediumcontaining water in an amount of about 30 to 35 percent by weight. Theslow flow rate occurs because: (1) the water must traverse a deep bed ofadsorbent particles; (2) the filter operates in a low pressureenvironment—only the pressure of the overlying water in the upperreservoir, typically several inches of water, is available to force thewater through the filter; and (3) the size of the adsorbent particlesare limited. Excessively large particles that would permit faster flowrates, would also have slower adsorption kinetics. This forces the useof relatively small particles (about 35 mesh) having faster adsorptionkinetics but greater flow restriction. In view of the above constraints,a liter of water normally takes about 5 to 10 minutes or more to processthrough the present day carafe filter.

It is desirable to have a high flow rate, gravity-flow carafe filterwhich is capable of intercepting the very small chlorine resistant cystssuch as Giardia and Cryptosporidium Parvum. It is also desirable toprovide a high flow rate, gravity-flow carafe filter with enhancedchlorine, taste and odor reduction as well as a filter that can absorbheavy metals such as lead. It is desirable to provide a high flow filterthat supports high flow with a 1 inch water column and that intercepts99.95 percent of 3 to 4 micron particles which makes it suitable forcyst reduction and which generally meets NSF Class 1 particle reductionrequirements. Mass production of carafe filters with simple equipmentand at low cost is a necessity.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide a fluidfilter that is capable of filtering contaminants from a fluid atrelatively high flow rates while providing a relatively low resistanceto fluid flow.

It is another object of the present invention to provide a fluid filtercapable of filtering chlorine resistant cysts such as Giardia andCryptosporidium Parvum.

It is yet another object of the present invention to provide a high flowrate carafe filter with enhanced chlorine, taste and odor reduction aswell as a filter that can absorb heavy metals such as lead.

It is still another object of the present invention to provide a carafefilter that can be mass produced with simple equipment and at low cost.

In accordance with the objects of the present invention, the foregoingprimary objective is realized by providing a low flow resistancecomposite filter medium for removing at least 99.95 percent ofparticulates of a size in the 3 to 4 micron range and dissolved chemicalcontaminants from a fluid comprising an adsorbent layer containing anadsorbent agent and a hydrophilic particulate intercepting layerdisposed adjacent to the adsorbent layer. The composite medium has amean flow pore diameter of about 1 to 10 microns, a bubble point ofabout 3 to 15 microns and an air permeability of about 0.5 to 7 litersper minute/cm² with a pressure drop of about 0.1 bar.

Other objects and advantages of the invention will be apparent from thefollowing detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings, not drawn to scale, include:

FIG. 1A, which is a sectional view of a first embodiment of thecomposite filter medium of the present invention;

FIG. 1B, which is a sectional view of a second embodiment of thecomposite filter medium of the present invention;

FIG. 1C, which is a sectional view of a third embodiment of thecomposite filter medium of the present invention;

FIG. 1D, which is a sectional view of a fourth embodiment of thecomposite filter medium of the present invention;

FIG. 1E, which is a sectional view of a fourth embodiment of thecomposite filter medium of the present invention;

FIG. 1F, which is a sectional view of a fourth embodiment of thecomposite filter medium of the present invention;

FIG. 2A, which is an isometric view of a flat sheet filter;

FIG. 2B, which is a partial cross-sectional view of the filterillustrated in FIG. 2A;

FIG. 3A, which is an isometric view of a basic cylindrical pleatedfilter;

FIG. 3B, which is an axial cross-sectional view of the filterillustrated in FIG. 3A;

FIG. 4A, which is a partially cut away isometric view of a basic spiralwound filter;

FIG. 4B, which is a cross-sectional view of a flow through filter mediumconfiguration for the filter illustrated in FIG. 4A;

FIG. 4C, which is a cross-sectional view of a tangential flow filtermedium configuration for the filter illustrated in FIG. 4A;

FIG. 5A, which is a cutaway perspective view of a pleated fluid filteremploying the composite filter medium of the present invention;

FIG. 5B, which is a top plan view of the filter illustrated in FIG. 5A;

FIG. 5C, which is a cross-sectional view of the pleated filterillustrated in FIG. 5B, taken along the line 5C-5C;

FIG. 5D, which is an end view of the filter illustrated in FIG. 5Ashowing the outlet end panel;

FIG. 5E, which is a partial cross-sectional view illustrating the edgesof the pleated filter medium joined together by insert molding in aframe;

FIG. 5F, which is partial cross-sectional view illustrating the edges ofthe pleated filter medium joined together by a hot-melt adhesive;

FIG. 6, which is a partial perspective view of a drainage directingsupport member; and

FIG. 7, which is a cross-sectional view of a carafe containing thefilter of the illustrated in FIGS. 5A through 5F.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

FIGS. 1A through 1F illustrate several embodiments of the compositefilter medium 10 of the present invention useful for removingcontaminants from a fluid, which generally comprises an adsorbent layer11 and a hydrophilic particulate intercepting layer 19. Referring to theembodiment illustrated in FIG. 1A, the adsorbent layer 11 comprises anadsorbent supporting web substrate 12 having a front surface 14 and aback surface 15. At least a portion of the front surface 14 is coatedwith adsorbent particles 16 and binder particles 18 which are fused tothe front surface 14 and to the adsorbent particles 16. The coating onthe adsorbent supporting web substrate 12 is obtained according to amethod which is described in co-pending U.S. patent application Ser. No.08/813,055, filed on Mar. 3, 1997, which is incorporated in its entiretyherein by reference. As basically described in the co-pendingapplication, the coating is obtained by preparing a mixture of adsorbentparticles and binder particles. Preferably, the binder particles have anaverage particle size not exceeding approximately 80 microns. Themixture is applied to part or all of the front surface 14 of theadsorbent supporting web substrate 12 to produce a loose powder coatingon the front surface. The loose powder coating is heated to at least theVicat softening temperature of the binder particles but below themelting temperature of the adsorbent supporting substrate 12 and theadsorbent particles to form softened binder particles 18. Pressure isapplied to the web substrate 12 to cause the softened binder particles18 to fuse with the adsorbent particles 16 and to the adsorbentsupporting web substrate 12.

The hydrophilic particulate intercepting layer 19 in the embodimentshown in FIG. 1A comprises a fiber supporting web substrate 20 having afront surface 21 positioned adjacent to the adsorbent supporting websubstrate 12 such that its front surface faces the back surface of theadsorbent supporting web substrate. A mixture of glass micro fibers 22and an FDA approved epoxy binder resin (not shown) is positioned betweenthe back side 15 of the adsorbent supporting web substrate 12 and thefront side 21 of the fiber supporting 20 web substrates. The glassfibers and binder resin may be adhered to one or both of the websubstrates 12, 20 with a hot melt adhesive, if desired, and the resin ispreferably treated to obtain a hydrophilic character. Also, thoseskilled in the art will now appreciate that the hydrophilic character ofthe particulate intercepting layer may be obtained in a number of waysincluding: adding surface active agents to the resin, glass micro fibersor supporting web substrates; post-treating the resulting compositemedium to provide a surfactant on its surfaces; or using intrinsicallyhydrophilic materials, such as Nylon micro fibers.

Of course those skilled in the art will now appreciate that the stepsfor making the first embodiment illustrated in FIG. 1A can be taken outof order. For example, the mixture of glass fibers 22 and resin may beprovided between the adsorbent supporting 12 and fiber supporting 20 websubstrates prior to the application of the adsorbent particles 16 andthe binder 18 on the adsorbent supporting web substrate 12 as describedabove. Laminated glass filter medium products made by Hollingsworth &Voss Company and marketed under the trademark HOVOGLAS may be used toform both the adsorbent supporting and fiber supporting web substrateshaving the glass micro fiber 22 and binder resin material therebetween.The adsorbent particles 16 and binder particles 18 may be applied to thelaminated glass filter medium product according to the method stepsdescribed above. Alternatively, sheet-like adsorbent productmanufactured and marketed by KX Industries under the trademark PLEKX maybe suitably modified by providing the glass micro fiber and resinmixture between the back, uncoated side of the adsorbent supporting websubstrate of the PLEX material and the front side of an adjacentlyplaced fiber supporting web substrate.

Generally, non-woven fibrous materials, such as high strength spunbondedpolyesters or polyolefins, wet or dry laid fibrous materials and porousmembranes can be used to form the adsorbent supporting 12 and fibersupporting 20 web substrates illustrated in the FIG. 1A embodiment.Preferably, the adsorbent supporting web substrate 12 is formed fromnon-woven fibrous materials such as the high strength spunbondedpolyesters and polyolefins and the fiber supporting web substrate 20 isformed from non-woven high strength spunbonded polyester. Materials suchas iodinated resin, activated carbon, activated alumina,alumina-silicates, ion-exchange resins, and manganese or iron oxides canbe used as adsorbent particles 16. Materials forming the binderparticles 18 typically include thermoplastics such polypropylene, linearlow density polyethylene, low density polyethylene and ethylene-vinylacetate copolymer.

Referring to the embodiment in FIG. 1B, the composite filter medium 10of FIG. 1A can be modified to include an overlying web substrate 30which has a surface 32 facing the front surface 14 of the particlesupporting web substrate 12. The coating of binder particles 18 fused tothe adsorbent particles and the surface 14 of the particles supportingweb substrate 12 may also be fused to the surface 32 of the overlyingweb substrate 30. The fusing of the binder particles 18 to the particlesupporting 12 and overlying 30 web substrates can be accomplishedaccording to the disclosure in co-pending U.S. application Ser. No.08/813,055. Essentially, after applying the mixture of particles to thesurface of the adsorbent supporting web substrate 12 to produce a powdercoating covering the portion of the surface thereof as described above,the overlying web substrate 30 is applied over the adsorbent supportingweb substrate 12 and powder coating thereon. Preferrably, the particlesupporting web substrate 12, the overlying web substrate 30, and powdercoating are heated to at least the Vicat softening temperature of thebinder particles but below the melting temperature of the materialforming the particle supporting web substrate, the overlying websubstrate, the adsorbent particles and the binder. Once the binderparticles are heated to the Vicat softening temperature, pressure isapplied to the particle supporting 12 and overlying 30 web substrates tocause the softened binder particles to fuse with the adsorbent particlesand the adjacent web substrates 12, 30. Those skilled in the art willappreciate that variations may be made in the process. For example, theadsorbent layer could be made by only heating the binder to the Vicatsoftening temperature before application thereof as a coating on theadsorbent supporting web substrate 12 and the application of theoverlying web substrate 30. The embodiment illustrated in FIG. 1B alsoincludes the fiber supporting web substrate 20 and the mixture of glassmicro fibers 22 and binder resin between the fiber supporting websubstrate 20 as described and illustrated with respect to the embodimentillustrated in FIG. 1A.

FIG. 1C illustrates a third embodiment of the composite filter medium ofthe present invention. In this embodiment, the filter medium illustratedin FIG. 1A is modified by disposing an intermediate web substrate 40between the glass micro fiber and resin mixture 22 and the back side 15of the adsorbent supporting web substrate 12. This embodiment may bemade by combining a single ply PLEKX sheet and the HOVOGLAS glass microfiber laminate.

FIG. 1D illustrates a fourth embodiment of the composite filter mediumof the present invention. The embodiment illustrated in FIG. 1C ismodified by including the overlying web substrate 30 which has thesurface 32 facing the surface 14 of the particle supporting websubstrate 12. The coating of binder particles 18 fused to the adsorbentparticles and the surface 14 of the adsorbent supporting web substrate12 are also fused to the surface 32 of the overlying web substrate 30 inthe same manner as illustrated in the embodiment of FIG. 1B. Thisembodiment may be made by simply combining a two ply PLEKX sheet and theHOVOGLASS glass micro fiber laminate.

FIGS. 1E through 1F illustrate other embodiments of the composite filtermedium. In FIG. 1E, the composite medium 210 comprises an adorbent layer11 formed by an adsorbent supporting web substrate 12 having adsorbentparticles 16 and binder particles 18 fused to the adsorbent particles 16and to the surface 14 of the supporting web substrate 12. Theparticulate intercepting layer 19 is formed from a hydrophilicmelt-blown micro fiber medium or any other suitable hydrophilic microfiber structure. Also, the particulate intercepting layer 19 may beformed from a hydrophilic membrane such as a Supor® porous membrane madeby Pall-Gelman Sciences of Ann Arbor, Mich. In the embodimentillustrated in FIG. 1F, the adsorbent layer also includes the overlyingweb substrate 30 and the binder particles 18 are fused to the surface 32of the overlying web substrate that faces the surface 14 of thesupporting web substrate 12. The particulate intercepting layer 19 maybe formed from a hydrophilic melt-blown micro fiber medium orhydrophilic porous membrane as described above.

In commercially available filtering water carafes, a pressure drop ofabout no more than about 1 to 3 inches of water is available to pushwater through a filter medium. To make a high flow filter with thecomposite filter medium 10 of the present invention which is suitablefor such end applications, the adsorbent layer 11 and the particulateintercepting layer 19 are selected from the materials described abovesuch that when tested with a COULTER Porometer II, the composite filtermedium has a mean flow pore diameter of about 1 to 10 microns, a bubblepoint in the range of about 3 to 15 microns and an air permeabilityrating of about 0.5 to 7 liters per minute/cm² with a pressure drop ofabout 0.1 bar. Mean flow pore diameter is the pore diameter at which 50percent of the flow is through pores that are larger and 50 percent ofthe flow is through pores that are smaller. Bubble point indicates thelargest pore size in the filter medium and air permeability is the flowrate of a gas through the sample at a given differential pressure. Thoseskilled in the art will appreciate that optimization of the compositefilter medium in the various illustrated embodiments to obtain the abovedescribed flow properties can be achieved by one or more of thefollowing: (1) varying the density, fiber diameter and basis weight ofthe glass micro fiber and resin mixture; (2) including or excluding theoverlying substrate, the intermediate substrate or both; (3) varying theadsorbent and binder particle sizes, concentrations and lay downweights; and (4) varying the properties of the web substrate by use ofdifferent materials.

All of the embodiments of the composite filter medium illustrated inFIGS. 1A through 1F can be incorporated into a variety of fluid filterconfigurations. Examples of such fluid filter configurations areillustrated in FIGS. 2A through 5F. Referring to FIGS. 2A and 2B, thecomposite filter medium 10 of the present invention may be used in asimple flat sheet filter apparatus 50. The flat-sheet filter 50 includesa rim 52 which defines a filtration area. The composite filter medium 10covers the filtration area defined by the rim 52. The edge 54 of themedium 10 is sealably affixed to the rim 10 by insert molding the rimover the edge 54 or by other suitable means such as affixation with abead of hot melt adhesive between the edge 54 and the rim 52. In theembodiment illustrated in FIGS. 2A and 2B, the filter is provided withan inlet support member 56 a on the inlet side 57 a of the filter medium10 and outlet support member 56 b on the outlet side 57 b of the filtermedium 10. The support members 56 a, 56 b extend from the rim into thefiltration area defined by the rim 52. Those skilled in the art willappreciate that only the inlet or outlet support member may be requiredfor a particular filtering application and that such members may beformed with any structural shape including that illustrated in FIG. 2A.A portion of the rim 52 on the outlet side 57 b of the filter medium 10may be provided with a groove 58 for sealably engaging with the rim of acontainer (not shown). To provide good sealing qualities, the rim may beformed from a resiliently deformable material such as rubber,thermoplastic elastomer or low density polyethylene. A portion of therim on an inlet side 57 a of the filter medium may be provided with anesting ridge 59. A plurality of filters 50 may be stacked such thatnesting ridge 59 of one filter may reside in the groove 58 of anadjacent filter and so on.

Referring to FIGS. 3A and 3B, the composite filtration medium 10 of thepresent invention may be used in a cylindrical pleated filter 60 forfiltering contaminants from a fluid. In FIG. 3A, the filter has a base62 (shown in dotted line) having an outlet opening therein (not shown).The filter 60 also includes a top 64 and a fluid permeable tube 66extending from the base 62 to the top 64. The end of the tube adjacentto the base 62 is connected with the outlet opening in the base. Thesheet-like filter medium 10 of the present invention may be sealablydisposed in a generally cylindrical configuration between the base 62and the top 64 and is provided with a plurality of outer radial pleatsthat extend lengthwise from the base 62 to the top 64 and a plurality ofinner radial pleats 72 located near the tube 66. The outer and innerradial pleats define a plurality of filtration panels 68. Fluid to befiltered may be caused to flow in a general direction from the outerradial pleats to the inner radial pleats and then to the tube asindicated by the flow arrows in the figures.

Referring to FIGS. 4A through 4C, the composite filter medium of thepresent invention may be used in a spiral wound filter configuration 80.The spiral wound filter configuration has a top 82 with a plurality ofperforations 84 therein for permitting fluid to enter the filter.Similarly, the filter has bottom 86 which also has a plurality ofperforations for permitting fluid to exit the filter. The top 82 andbottom 86 of the filter are held in a spaced apart relationship by asupport tube 88 which extends from the top to the bottom. The sheet-likefilter medium of the present invention 10 having a top edge 90 aadjacent to the top and a bottom edge 90 b adjacent to the bottom isspirally wound around the support tube 88. A cylindrical housing 92extending from the top to the bottom is provided to cover and enclosethe spirally wound filter medium 10.

In the embodiment in FIG. 4B, the fluid is permitted to flowtangentially relative to the filter medium 10 as shown by the flowarrows. However, this arrangement is generally only effective forchemical and heavy metals reduction and is not highly effective for thereduction of small particles. Referring to FIG. 4C, to force the fluidto flow through the filter medium before exiting the filter at thebottom 86 as shown by the flow arrows, alternating adjacent edges of thespiral wound filter medium are provided with barriers 94. The barriers94 may be formed from a hot melt adhesive, polyurethane or othersuitable material.

Referring to FIGS. 5A through 5F, the composite filter medium 10 of thepresent invention may be used to form a pleated panel filter 100 forfiltering contaminants from a fluid. The panel filter 100 includes anoutlet end panel 102 having an opening 104 therein. The composite filtermedium 10 sealably covers the opening 104 of the outlet end panel. Thecomposite filter medium 10 is pleated so as to have a first outwardpleat 106 a located remotely from the outlet end panel, an inward pleat106 b located closely to the outlet end panel, and a second outwardpleat 106 c located remotely from the outlet end panel. The pleats 106a-106 c collectively define four filter medium panels. A first panel 108a extends between the outlet end panel 102 and the first outward pleat106 a. A second panel 108 b extends from the first outward pleat 106 ato the inward pleat 106 b. A third panel 108 c extends from the inwardpleat 106 b to the second outward pleat 106 c. Finally, a fourth panel108 d extends from the second outward pleat 106 c to the outlet endpanel 102.

When the panels 108 a-108 d are made to be relatively large due to thedesire to have a high surface area of filter medium in the filter 100,the filter 100 may be provided with one or more drainage support membersto prevent collapsing of the filter medium upon itself. If unsupported,collapsed filter surfaces would close and could increase the pressuredrop across the filter and undesirably restrict fluid flow through thefilter. As illustrated in FIGS. 5A and 5C, the filter is provided with afirst drainage support member. 110 a disposed between the first andsecond filter panels 108 a, 108 b, a second drainage support member 110b disposed between the second and third filter panels 108 b, 108 c and athird drainage support member 110 c disposed between the third andfourth filter panels 108 c, 108 d.

Referring to FIG. 6, the support members, such as the first supportmember 110 a, may comprise a rigid or semi-rigid sheet 112 including oneor more elongated ribs 114 extending from the surface of the member. Themembers may be disposed between the panels such that the elongated ribs112 are aligned to point substantially towards the opening 104 in theoutlet end panel 102 to direct the flow of fluid towards the opening104. Apertures 116 may be provided in the sheet between the ribs 114 topermit fluid flow from one side of the drainage support member to theother. Materials sold by Applied Extrusion Technologies or Middletown,Del. under the trademark DELNET or by Amoco Fabrics Company of Atlanta,Ga. under the trademark VEXAR may be used as the drainage supportmembers.

Referring to FIGS. 5A, 5B, 5E and 5F, the filter is further providedwith a frame 120 extending from the outlet end panel 102. To sealablycover the opening in the outlet end panel 102, the edges 122 a, 122 b ofthe filter medium 10 may be attached to and supported by the frame 120.Alternatively, to sealably cover the opening in the outlet end panel102, the respective edges 122 a, 122 b of the filter medium may bebonded together with a bead of hot melt adhesive 124.

Any of the above described filters employing the filter medium of thepresent invention can be used in a gravity flow, filtering carafe. Asshown in FIG. 7, such a carafe 130 is divided into an upper reservoir132 and a lower reservoir 134 by a partition 136 that is provided with afilter receiving receptacle 138 having an opening (not shown) in thebottom thereof. A filter, such as the filter illustrated in FIGS. 5Athrough 5F, is inserted into the receptacle 138 so that it is supportedon its outlet end panel 102 in the receptacle 138. A gasket (not shown)may be provided between the outlet end panel 102 and the bottom of thereceptacle 138 to seal the upper reservoir from the bottom reservoir134. When a quantity of water is poured into the upper reservoir 132, itflows under gravity through the filter containing the filter medium ofthe present invention into the lower reservoir 134. Filtered water maybe poured from the lower reservoir via outlet 140.

As can be seen by the foregoing discussion, the filter medium of thepresent invention is very useful for making filters for water filteringcarafes because it permits the use of filter configurations capable ofproviding high filtration flow rates with the several inches of waterpressure that is typically available in such carafe filters. The highflow rate is a result of a substantially increased cross-sectionalfilter flow area (up to about 20 times) as compared to a traditionaltrapezoidal carafe filter element. Accordingly, because a greatercross-sectional flow area may be provided, the adsorbent bed depthpresented to the flow of fluid can be reduced by up to 60 times ascompared to conventional carafe filter elements.

Also, to take advantage of the increased cross-sectional area providedby the filter medium of the present invention, the size of adsorptiveparticles can be reduced from the size currently in use withconventional carafe filters. Because smaller particles provide betteradsorption kinetics, the overall performance of the filter of thepresent invention can be greatly improved as compared to theconventional carafe filter under the same pressure drop and flow rateconditions. Use of small adsorbent particles that are more effectiveallows a substantial reduction in the volume of adsorbent required tomeet performance goals. The low flow resistance provided by the filtermedium of the present invention can be used to intercept very smallparticles, such as those within the 3 to 4 micrometer range, a rangewhich is required to intercept waterborne pathogenic oocysts such asGiardia and Cryptosporidium Parvum.

As can be seen from the foregoing detailed description and drawings, thefilter of the present invention permits high filtration flow rates to beobtained in low pressure environments, such as those typically found ingravity flow carafe filters. Although the filtering apparatus has beendescribed with respect to one or more particular embodiments; it will beunderstood that other embodiments of the present invention may beemployed without departing from the spirit and scope of the presentinvention. Hence, the present invention is deemed limited only by theappended claims and the reasonable interpretation thereof.

1. A low flow resistance composite filter medium for removing at least99.95 percent of particulates at a size in the 3 to 4 micron range anddissolved chemical contaminants from a fluid, the composite filtermedium comprising: an adsorbent layer containing at least one adsorbentagent; a hydrophilic particulate intercepting layer disposed adjacent tothe adsorbent layer; and wherein the composite filter medium has a meanflow pore diameter of about 1 to 10 microns, a bubble point of about 3to 15 microns and an air permeability of about 0.5 to 7 liters perminute/cm2 with a pressure drop of about 0.1 bar.
 2. The compositefilter medium of claim 1, wherein the adsorbent layer further comprisesan adsorbent supporting web substrate having a surface coated with amixture of adsorbent particles and binder particles fused to the surfaceand to the adsorbent particles.
 3. The composite filter medium of claim2, wherein the material forming the adsorbent particle supporting websubstrate web is a non-woven fibrous material selected from the groupconsisting of spun bonded polymers, wet laid fibrous materials and drylaid fibrous materials.
 4. The composite filter medium of claim 2,wherein the material forming the adsorbent particles is selected fromthe group consisting of iodinated resin, activated carbon, activatedalumina, alumina-silicates, ion exchange resins, manganese oxide andiron oxide.
 5. The composite filter medium of claim 2, wherein thematerial forming the binder particles is a thermoplastic selected fromthe group consisting of polyolefins, polypropylene, low densitypolyethylene, linear low density polyethylene, ethylene vinyl acetateand high density polyethylene.
 6. The composite filter medium of claim2, wherein an overlaying web substrate is provided adjacent to theadsorbent supporting web substrate on its front side and wherein thebinder particles are also fused to the overlaying web substrate.
 7. Thecomposite filter medium of claim 1, wherein the hydrophilic particulateintercepting layer comprises a fiber supporting web substrate positionedadjacent to the adsorbent layer and a micro fiber and resin mixturedisposed between the adsorbent layer and the fiber supporting websubstrate.
 8. The composite filter medium of claim 7, wherein anintermediate web substrate is disposed between the micro fiber and resinmixture and the adsorbent layer.
 9. The composite filter medium of claim7, wherein the material forming the fiber supporting web substrate webis a non-woven fibrous material selected from the group consisting ofspun bonded polymers, wet laid fibrous materials and dry laid fibrousmaterials.
 10. The composite filter medium of claim 2, wherein thehydrophilic particulate intercepting layer comprises a fiber supportingweb substrate positioned adjacent to the adsorbent supporting websubstrate and a micro fiber and resin mixture disposed between theadsorbent supporting web substrate and the fiber supporting websubstrate.
 11. The composite filter medium of claim 10, wherein anintermediate web substrate is disposed between the micro fiber and resinmixture and the adsorbent supporting web substrate.
 12. The compositefilter medium of claim 10, wherein an overlaying web substrate isprovided adjacent to the adsorbent supporting web substrate on its frontside and wherein the binder particles are also fused to the overlayingweb substrate.
 13. The composite filter medium of claim 12, wherein anintermediate web substrate is disposed between the micro fiber and resinmixture and the adsorbent supporting web substrate.
 14. The compositefilter medium of claim 13, wherein the material forming the fibersupporting web substrate web is a non-Woven fibrous material selectedfrom the group consisting of spun bonded polymers, wet laid fibrousmaterials and dry laid fibrous materials.
 15. The composite filtermedium of claim 1, wherein the hydrophilic particulate interceptinglayer comprises a hydrophilic melt blown micro fiber medium.
 16. Thecomposite filter medium of claim 2, wherein the hydrophilic particulateintercepting layer comprises a hydrophilic melt blown micro fibermedium.
 17. The composite filter medium of claim 16, wherein anoverlaying web substrate is provided adjacent to the adsorbentsupporting web substrate on its front side and wherein the binderparticles are also fused to the overlaying web substrate.
 18. Thecomposite filter medium of claim 1, wherein the hydrophilic particulateintercepting layer comprises a hydrophilic porous membrane.
 19. Thecomposite filter medium of claim 2, wherein the hydrophilic particulateintercepting layer comprises a hydrophilic porous membrane.
 20. Thecomposite filter medium of claim 19, wherein an overlaying web substrateis provided adjacent to the adsorbent supporting web substrate on itsfront side and wherein the binder particles are also fused to theoverlaying web substrate.
 21. A filter for removing 99.95 percent ofparticulates of a size in the 3 to 4 micron range and dissolved chemicalcontaminants from fluid, the filter comprising: a rim defining afiltration area within the rim; a sheet-like composite filter mediumdisposed within the filtration area of the rim and having edges sealablyaffixed to the rim, wherein the sheet-like composite filter mediumfurther comprises: an adsorbent layer containing an adsorbent agent; ahydrophilic particulate intercepting layer disposed adjacent to theadsorbent layer; and wherein the composite filter medium has a mean flowpore diameter of about 1 to 10 microns, a bubble point of about 3 to 15microns and an air permeability of about 0.5 to 7 liters per minute/cm²with a pressure drop of about 0.1 bar; and at least one support memberextending from the rim into the filtration area.
 22. The filter of claim21, wherein a portion of the rim on an outlet side of the filter mediumis provided with a groove for sealably engaging with the rim of acontainer.
 23. The filter of claim 22, wherein the rim is formed from aresiliently deformable material.
 24. A cylindrical pleated filter forremoving 99.95 percent of particulates of a size in the 3 to 4 micronrange and dissolved chemical contaminants from fluid, the filtercomprising: a base having an outlet opening therein; a top; a fluidpermeable tube extending from the base to the top, the tube having anend engaged with the outlet opening in the base; a sheet-like compositefilter medium sealably disposed in a generally cylindrical configurationabout the porous tube between the base and top, the medium furtherhaving a plurality of outer radial pleats extending from the base to thetop and a plurality of inner radial pleats adjacent to the tube, theouter and inner radial pleats defining a plurality of filtration panels,and wherein the composite filter medium further comprises: an adsorbentlayer containing an adsorbent agent; a hydrophilic particulateintercepting layer disposed adjacent to the adsorbent layer; and whereinthe medium has a mean flow pore diameter of about 1 to 10 microns, abubble point of about 3 to 15 microns and an air permeability of about0.5 to 7 liters per minute/cm² with a pressure drop of about 0.1 bar 25.A spiral wound filter for removing 99.95 percent of particulates of asize in the 3 to 4 micron range and dissolved chemical contaminants froma fluid, the filter comprising: a top having a plurality of perforationstherein; a bottom having a plurality of perforations therein; a supporttube extending from the top to the bottom; a sheet-like composite filtermedium having a top edge adjacent to the top and a bottom edge adjacentto the bottom and being spirally wound around the support tube, whereinthe composite filter medium further comprises: an adsorbent layercontaining an adsorbent agent; a hydrophilic particulate interceptinglayer disposed adjacent to the adsorbent layer; and wherein the mediumhas a mean flow pore diameter of about 1 to 10 microns, a bubble pointof about 3 to 15 microns and an air permeability of about 0.5 to 7liters per minute/cm² with a pressure drop of about 0.1 bar.
 26. Thefilter according to claim 25, wherein alternating edges of the spiralwound filter medium are provided with a barrier to force fluid to flowthrough the composite filter medium before exiting the filter.
 27. Apleated panel filter for removing 99.95 percent of particulates of asize in the 3 to 4 micron range and dissolved chemical contaminants froma fluid, the filter comprising: an outlet end panel having an openingtherein; a sheet-like composite filter medium capable of sealablycovering the opening of the outlet end panel, wherein the sheet-likecomposite filter medium is pleated so as to have a first outward pleatlocated remotely from the outlet end panel, an inward pleat locatedclosely to the outlet end panel, and a second outward pleat locatedremotely from the outlet end panel, wherein the pleats define fourfilter medium panels comprising a first panel extending between theoutlet end panel and the first outward pleat, a panel extending from thefirst outward pleat to the inward pleat, a third panel extending fromthe inward pleat to the second outward pleat and a fourth panelextending from the second outward pleat to the outlet end panel, whereinthe composite filter medium further comprises: an adsorbent layercontaining an adsorbent agent; a hydrophilic particulate interceptinglayer disposed adjacent to the adsorbent layer; and wherein the mediumhas a mean flow pore diameter of about 1 to 10 microns, a bubble pointof about 3 to 15 microns and an air permeability of about 0.5 to 7liters per minute/cm² with a pressure drop of about 0.1 bar.
 28. Thefilter according to claim 27, wherein the filter is further providedwith at least one drainage support member disposed between adjacentfilter medium panels.
 29. The filter according to claim 28, wherein thedrainage support member comprises a sheet having a plurality ofelongated ribs extending therefrom and a plurality of apertures disposedbetween the elongated ribs.
 30. The filter according to claim 27,wherein the filter is further provided with a first drainage supportmember disposed between the first and second filter medium panels, asecond drainage support member disposed between the second and thirdfilter medium panels and a third drainage support member disposedbetween the third and fourth filter medium panels.
 31. The filteraccording to claim 27, wherein the filter is further provided with aframe extending from the outlet end panel and wherein the filter mediumincludes at least one edge supported by the frame.
 32. A filtrationdevice comprising: an unfiltered fluid inlet surface, through whichunfiltered fluid may enter the filtration device; a first filter mediain fluid communication with said unfiltered fluid inlet surface, saidfirst filter media being spirally wound and being positioned withrespect to said unfiltered fluid inlet surface so that unfiltered fluidentering the filtration device through said unfiltered fluid inletsurface is directed to flow radially inward and through said firstfilter media; a core in fluid communication with said first filtermedia, said core having a surface that defines apertures, said corebeing positioned with respect to said spirally wound first filter mediaso that filtered fluid flowing radially inward from said first filtermedia flows into said core, said core having a first end and a secondend with the first end being open so that filtered fluid may exit thecore and with the second end being closed so that the flow of fluidthrough the second end is prevented; and a filtered fluid outlet influid communication with the first end of said core so that filteredfluid flowing from the first end of said core exits the filtrationdevice through said filtered fluid outlet.
 33. A filtration devicecomprising: an unfiltered fluid inlet, through which unfiltered fluidmay enter the filtration device; a core in fluid communication with saidunfiltered fluid inlet, said core having a surface defining aperturestherein so that unfiltered fluid may flow from said unfiltered fluidinlet and radially outward through said core, said core having a firstend and a second end, wherein the first end is open so that unfilteredfluid may enter said core and wherein the second end is closed so thatflow of fluid through the second end is prevented; a first filter mediain fluid communication with said core, said filter media being spirallywound around the surface of said core so that fluid flowing from saidcore may flow radially outward through the apertures and into said firstfilter media; and a filtered fluid outlet surface in fluid communicationwith said first filter media so that filtered fluid from said firstfilter media may exit the filtration device through said filtered fluidoutlet surface.
 34. A filtration device comprising: a housing definingan interior volume, an inlet for allowing fluid to be filtered to enterthe volume, and an outlet for filtered fluid to exit the volume; a corelocated within the volume, said core defining a chamber, at least oneaperture allowing fluid communication through said core and into thechamber, and an exit orifice in fluid communication with the outlet; anda spirally wound filtration media located within the volume andconfigured so that fluid entering the volume from the inlet directed toflow radially inward and through the filtration media, through saidcore, and into the chamber and out of the outlet.
 35. A multistagefilter comprising: an inlet for liquid flow and an outlet for liquidflow; a first filter stage in fluid communication with said inlet, saidfirst filter stage comprising a material that removes microorganisms; asecond filter stage in fluid communication with said outlet, said secondfilter stage comprising activated carbon; and said second filter stagebeing located at a position that allows liquid to pass through saidfirst filter stage, prior to passing through said second filter stage.36. A multistage process for filtering impurities from a liquid, saidprocess comprising the steps of: supplying liquid to a filter; removingat least a portion of the microorganisms from said liquid supply in afirst filtering step; and then removing at least a portion of theorganics and other non-biological components in a second filtering stepusing activated carbon.
 37. A multistage liquid filter, comprising: aninlet for liquid flow and an outlet for liquid flow; a first filterstage in fluid communication with said inlet, said first filter stagecomprising a material that removes microorganisms; and a second filterstage in fluid communication with said outlet, said second filter stagecomprising activated carbon, said second filter stage being located at aposition that allows liquid to pass through said first filter stageprior to passing through said second filter stage.